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941.
Torsion problems for a cylinder with a rectangular hole and a rectangular cylinder with a crack 总被引:1,自引:0,他引:1
Using the method of singular integral equation and the crack-cutting technique, the rigorous solutions are obtained for a
cylinder with a rectangular hole and a rectangular cylinder with a crack, which exactly satisfy the boundary conditions and
the conditions at the corner points. After that the torsional rigidities and the stress intensity factors at the crack tip
are determined. Next, for the doubly connected circular cylinder with a rectangular hole the expressions for the singular
stresses around the concave corner points are derived and the generalized stress intensity factors are then defined. Since
the crack-cutting technique is used in this paper, the solution of the matching rectangular cylinder is also obtained and
its numerical results coincide with those in references. Thus the method proposed here is verified.
The project supported by National Natural Science Foundation of China 相似文献
942.
943.
A comparative study of the wakes behind cylinders with grooved and smooth surfaces was performed with a view to understand the wake characteristics associated with the adult Saguaro cacti. A low-speed recirculation water channel was established for the experiment; the Reynolds number, based on the free-stream velocity and cylinder diameter (D), was kept at ReD=1500. State-of-the-art time-resolved particle image velocimetry (TR-PIV) was employed to measure a total of 20 480 realizations of the wake field at a frame rate of 250 Hz, enabling a comprehensive view of the time- and phase-averaged wake pattern. In comparison to the wake behind the smooth cylinder, the length of the recirculation zone behind the grooved cylinder was extended by nearly 18.2%, yet the longitudinal velocity fluctuation intensity was considerably weakened. A global view of the peaked spectrum of the longitudinal velocity component revealed that the intermediate region for the grooved cylinder, which approximately corresponds to the transition region where the shear layer vortices interact, merge and shed before the formation of the Karman-like vortex street, was much wider than that for the smooth one. The unsteady events near St=0.3-0.4 were detected in the intermediate region behind the grooved cylinder, but no such events were found in the smooth cylinder system. Although the formation of the Karman-like vortex street was delayed by about 0.6D downstream for the grooved cylinder, no prominent difference in the vortex street region was found in the far wake for both cylinders. The Proper Orthogonal Decomposition (POD) method was used extensively to decompose the vector and swirling strength fields, which gave a close-up view of the vortices in the near wake. The first two POD modes of the swirling strength clarified the spatio-temporal characteristics of the shear layer vortices behind the grooved cylinder. The small-scale vortices superimposed on the shear layers behind the grooved cylinder were found to be generated and convected downstream in the same phase, which would significantly reduce the fluctuating force on the cylinder surface. 相似文献
944.
为克服单线阵难以无源测距、测速的缺点,提出了利用目标辐射低频声场干涉结构和波导不变量的运动单线阵无源测距、测速方法。定义了运动目标的距离距变率比(目标距离与距离变化率的比值),并利用与目标辐射声场的时间-频率干涉结构和波导不变量相关的变量来表征距离距变率比。根据此定义,通过对目标辐射声场的时间-频率干涉结构图进行Radon变换等处理,实现对距离距变率比的估计。利用所估计的距离距变率比,结合平台速度、目标方位角和目标航向角实现对目标距离和速度的同时估计。仿真实验验证了所提方法在测距、测速时的正确性和有效性。结果表明:所提方法在目标航向角较大时有较高的距离、速度估计精度;同时,目标方位估计误差越小,所提方法的距离、速度估计精度越高。 相似文献
945.
946.
Chunning Ji Zhong Xiao Yuanzhan Wang Huakun Wang 《International Journal of Computational Fluid Dynamics》2013,27(4):207-221
A direct numerical simulation of two-dimensional (2D) flow past an elastically mounted circular cylinder at low Reynolds number using the fictitious domain method had been undertaken. The cylinder motion was modelled by a two degree-of-freedom mass–spring–damper system. The computing code was verified against a benchmark problem in which flow past a stationary circular cylinder is simulated. Then, analyses of vortex-induced vibration (VIV) responses, drag and lift forces and the phase and vortex structures were carried out. Results show that the cylinder's non-dimensional cross-flow response amplitude reaches its summit of 0.572 in the ‘lock-in’ regime. The ‘2S’, instead of the ‘2P’, vortex shedding mode is dominated in the ‘lower’ branch for this 2D low-Re VIV. A secondary oscillation is observed in the lift force when ‘lock-in’ occurs. It is shown that this secondary component changes the phase, offset the energy input by the primary component and thus reduces the cylinder responses. Effects of the Skop–Griffin parameter on cylinder responses were also investigated. 相似文献
947.
Control of mean and fluctuating forces on a circular cylinder at high Reynolds numbers 总被引:2,自引:0,他引:2
A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 × 104 to 1.0 × 105. The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized
by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the
cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in
an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local
changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak
value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points
of view.
The project supported by the National Natural Science Foundation of China (10172087 and 10472124).
The English text was polished by Yunming Chen. 相似文献
948.
This paper numerically investigates the effectiveness of the control of steady suction on a stationary circular cylinder with several isolated suction holes on the surface at a subcritical Reynolds number. The control effectiveness as a function of the azimuthal position, spanwise spacing and suction flow rate of the suction holes on the control of the aerodynamic forces on the cylinder and the suppression of alternate vortex shedding are taken into account. The study of the azimuthal location of the suction holes indicates that azimuthal angles of θ=90° and 270°, which are close to the separation point, provide the most substantial decreases in the aerodynamic forces. When restricted to the most effective azimuthal angle, a remarkable control effectiveness can be achieved when the axial spacing between two neighboring suction holes is less than a minimum value even under a small suction momentum coefficient. However, if the axial spacing exceeds the minimum spacing, the control effectiveness will not be saturated even under a very large suction momentum coefficient. Thus, the cause of the effective aerodynamic force control is suggested to be a result of obvious three-dimensional phenomenon in the near wake, which is characterized by the generation of a convergent flow between two neighboring suction hole sections and a stronger, larger three-dimensional vortex pair adjacent to the convergent flow. It has been suggested that this strongly three-dimensional flow pattern is induced by the strong interaction between two neighboring but counter-rotating three-dimensional vortices separately produced by two neighboring suction holes. Moreover, the effects of such three-dimensional flow patterns are investigated in detail based on variations in the flow field and sectional aerodynamic forces in different cross sections. Finally, the upper limit of the axial spacing between two neighboring suction holes to form such a three-dimensional flow pattern is suggested to be between 0.75 D and 1.5 D when the suction flow rate exceeds a certain value. 相似文献
949.
950.
本文采用流场显示方法研究单圆柱在非定常流动中的涡旋脱落规律。实验结果表明:在不同的KC数(KC=U∞T/D)下,非常圆柱绕流的涡旋脱落特性是不相同的,一般随KC数值的增加,其涡旋脱落对数也增加,但有明显的阶梯性,同时圆柱分离点的周期变化后于流场的变化。 相似文献